Fast and Reversibly Swtichable Wettability Induced by Photothermal Effect

Abstract

We prepared the smart surfaces capable of fast switching between hydrophilic and hydrophobic states by visible light irradiation. For this purpose, we first prepared rough surfaces on a silicon wafer by using the layer-by-layer (LBL) deposition. The substrate was alternately immersed into an aqueous solution with poly(allylamine hydrochloride) (PAH) and another aqueous solution containing SiO2 nanoparticles having diameter of ~ 11nm. Then, the substrate was successively immersed into another solution having poly(styrene sulfonic acid) (PSS) and an aqueous solution with gold nanoparticles having diameter of ~50 nm. Finally, thermally responsive poly(N-isopropylacrylamide) (PNIPAM) film was grafted on (SiO2/PAH)10(PSS/Au)20 surface by using surface-initiated atom transfer radical polymerization. Since the PNIPAM/water mixture system shows the phase behavior with lower critical solution temperature, the wettability of the fabricated surface is changed with the film temperature. The temperature of the fabricated film in this study was controlled by the heat generation arising from the photothermal effect of Au nanoparticles in the presence of visible light. We found that the wettability of the fabricated surface was fast switched reversibly between hydrophilic and hydrophobic properties without and with visible light illumination on the film. The surfaces introduced in this study could be used in functional textiles, intelligent microfluidic switching machine, controllable drug releases, and light-responsive filters.